The present invention relates to a coil component including a winding wire portion which is formed by winding a wire having electrical conductivity into a plurality of layers by alignment winding, to a powder-compacted inductor incorporating the coil component and to a winding method for the coil component.
In the past, it has been known that an inductor may be configured with a powder-compacted body formed by compression-molding metal magnetic powder in which an air-core coil is embedded (hereinafter, referred to as a “powder-compacted inductor”). For example, see Japanese Patent Publication Numbers JP 2003-229311 and JP 2003-168610 described below. While this powder-compacted inductor has a small size and a short stature, it also has excellent direct-current superimposing characteristics and low electric current resistance. As a result, this powder-compacted inductor has been utilized as an inductor for a power supply of mobile-type electronic equipment, such as a notebook personal computer for which miniaturization and flattening are highly desirable.
An air-core coil of a multi-layer winding used for such a powder-compacted inductor also requires miniaturization and height-shortening. As winding methods for such a multi-layer winding coil, an alignment winding method and an α winding method have been generally used.
Alignment winding is generally construed as a technique in which, while one end (an end from which winding starts) of a wire is fastened to an inner wall portion of one side of a winding frame of a winding machine, the other end of the wire is sequentially fed. Thus, the wire is wound such that the adjacent wires closely contact each other. After a first wound layer (an inner circumference wound layer) is formed by winding the wire from the inner wall portion of one side of the winding frame to the inner wall portion of the other side of the winding frame, a second wound layer is formed around an outer circumference portion of the first wound layer. Specifically, because the wire is wrapped around the outer circumference portion of the first wound layer by a mechanism that reverses the wire feed direction at the inner wall portion of the other side of the winding frame, the wire is wound from the inner wall portion of the other side of the winding frame to the inner wall portion of the one side of the winding frame at the outer circumference portion so that the second wound layer is formed. After the second wound layer is formed, a third wound layer is formed at the outer circumference portion of the second wound layer. Specifically, because the wire is wrapped around the outer circumference portion of the second wound layer by the mechanism that reverses the wire feed direction at the inner wall portion of the one side of the winding frame, the wire is wound from the inner wall portion of the one side of the winding frame to the inner wall portion of the other side of the winding frame at the outer circumference portion of the second wound layer so that the third wound layer is formed. Thereafter, according to procedures similar to those discussed above, respective wound layers up to a final wound layer (an outermost circumference wound layer) are formed.
On the other hand, α winding is generally construed as a technique in which, while making an intermediate portion of the wire touch a center portion of a winding shaft of a winding machine, the wire is wound while the two ends of the wire are fed. For example, see Japanese Patent Publication Number JP S62-23346 described below. After a first wound layer is formed by winding the wires from the center portion of the winding shaft toward each of the inner wall portions of one side of a winding frame and the other side of the winding frame, a second wound layer is formed. Specifically, because the wire is wrapped around an outer circumference portion of the first wound layer by a mechanism that respectively reverses the wire feed directions at the inner wall portions of the one side of the winding frame and the other side of the winding frame, the wires are wound and aligned from the inner wall portions of the one side of the winding frame and the other side of the winding frame toward the center portion of the winding shaft at the outer circumference portion of the first wound layer so that the second wound layer is formed. After the second wound layer is formed, a third wound layer is formed at the outer circumference portion of the second wound layer. Specifically, because the wire is wrapped around the outer circumference portion of the second wound layer by the mechanism that respectively reverses the feed directions of the wires at the center portion of the winding shaft, the wires are wound from the center portion of the winding shaft toward each of the inner wall portions of the one side of the winding frame and the other side of the winding frame at the outer circumference portion of the second wound layer so that the third wound layer is formed. Thereafter, according to procedures similar to those discussed above, respective wound layers up to a final wound layer are formed.
In case of a wire being wound by α winding, because both end portions of the wire are extended and extracted outwardly from the outer circumference portion of the coil, there is an advantage that handling becomes easy when connecting both ends of the wire to the respective terminals. However, in α winding, when reversing the feed directions of the wires at the center portion of the winding shaft, the alignment of the wires is easily disturbed. Thus, for a coil subjected to α winding, there is a tendency that the wire occupancy (the ratio of the sum of the cross-sectional areas of the respective wires occupying the cross-sectional area of the coil) becomes low.
On the other hand, in a coil subjected to alignment winding, one end (an end from which winding starts) of the wire fastened to the inner wall portion of one side of a winding frame when being wound is pulled out from the inner circumference side of the coil to the outer circumference side across the end surface of one side in the axis direction of the coil. Because there is a problem that the height of the coil may increase by as much as the diameter of this pulled-out wire, is difficult to improve the wire occupancy for the coil.